Stenella Population Abundance Monitoring (SPAM98) was a marine mammal assessment survey conducted in the eastern tropical Pacific Ocean (ETP). The survey was carried out with three vessels. The activities of the other two vessels, NOAA Ship DAVID STARR JORDAN and UNOLS Ship ENDEAVOR, are covered in separate Reports.

FOREIGN PARTICIPANTS:

Instituto National de la Pesca (INP), Mexico Armada de Guatemala

ITINERARY:

The cruise consisted of five legs with four to five day port calls between each leg. Research was conducted in the international waters of the ETP and in the coastal waters of Mexico, Guatemala, El Salvador, Costa Rica, Panama, Colombia, and France (Clipperton Island).

31 JUL

Depart San Diego, CA

31 JUL - 16 AUG

Leg I

16 AUG - 21 AUG

Puerto Quetzal, Guatemala

21 AUG - 08 SEP

Leg II

08 SEP - 13 SEP

Panama City, Panama

13 SEP - 07 OCT

Leg III

07 OCT - 12 OCT

Manzanillo, Mexico

12 OCT - 09 NOV

Leg IV

09 NOV - 14 NOV

Manzanillo, Mexico

14 NOV - 09 DEC

Leg V

09 DEC

Arrive San Diego, CA

OBJECTIVES:

The project was a multidisciplinary survey with the primary objective being to estimate the abundance of dolphins affected by the ETP purse-seine fishery for yellow-fin tuna, Thunnus albacares. The survey’s design targeted the depleted stocks of spinner dolphins, Stenella longirostris orientalis (the eastern stock), and spotted dolphins, Stenella attenuata (the northeastern offshore stock). Additional data and samples were collected in order to characterize the physical and biological characteristics of the ETP pelagic ecosystem. This year’s 1998 survey was the first of three (1998-2000) that are planned.

STUDY AREA:

The study area extended from the US/Mexico border, south to the territorial waters of Peru, bounded on the east by the continental shores of the Americas, and to the west to Hawaii (Fig. 1). Past studies indicate this region encompasses the entire distribution of the dolphin stocks most affected by the fishery. The study area was divided into four sampling strata which received varying levels of survey effort: the core area, the outer area, and north and south coastal areas (Fig.1).

PROCEDURES:

Dolphins were surveyed using standard line transect methods. Observers maintained a visual watch for marine mammals during daylight hours (approximately 0600 to 1800) using two 25 X 150 power "bigeye" binoculars mounted on the port and starboard sides of the ship’s flying bridge. An auxilliary 25 X 150 pair of binoculars were also mounted on the flying bridge for periodic use during sightings or making bird counts. Total binocular height above the water was 10.44 meters, giving a maximum ship-to-horizon sighting distance of approximately 11.5 km (6.2 nm).

The marine mammal survey was conducted by six observers rotating through three watch positions: port binoculars, data recorder, and starboard binoculars. Observers shifted positions every 40 minutes. At least one identification specialist with previous experience in the ETP was on watch at all times.

The observer at the port binoculars surveyed the area between 10° right and 90° left of the trackline. The observer at the starboard binoculars surveyed the area between 10° left and 90° right of the trackline. Thus, the area 10° to either side of the trackline was covered by both bigeye observers while more lateral regions were covered by one observer or the other. Using unaided eye and 7X binoculars, the data recorder searched the entire 180° forward of the ship, with effort focused on the trackline and the area from the ship out to 300 meters (the "blind" area in the 25X).

The data recorder entered sighting, weather and effort information into a laptop computer on the flying bridge using the software program "WinCruz", developed at Southwest Fisheries Science Center (SWFSC). The computer was linked to the ship’s global positioning system (GPS) to record time and position.

For each marine mammal sighting, bearing (using an azimuth ring on the binocular mount to measure angle) and distance (using a reticle scale inscribed in the eyepiece) were recorded, along with the initial sighting cue. Schools were approached if they were within three nautical miles of the trackline. Observers identified cetaceans, to the level of species/stock when possible, and then made independent estimates of school size. If more than one taxon was present, percent composition for each was estimated independently by each observer.

Seabird observations were conducted concurrently with mammal observations using standard strip transect methods. A single bird observer recorded identity and behavior for all seabirds within 300 m of one side of the ship. Mammal observers on the bigeyes detected feeding flocks within 3.7 km (2 nm) on either side of the ship, and the bird observer recorded size and species composition using the third pair of bigeye binoculars.

When sighted, identification and position of sea turtles were recorded. Turtles close to the ship’s trackline were captured using nets or a small boat. Turtles were measured, weighed, and flipper-tagged and blood samples for genetic and hormonal studies were collected. All turtles were subsequently released.

Cetacean tissue samples for genetic analysis were obtained on an opportunistic basis using hollow-tipped darts fired from a crossbow. Samples were collected from the bow of the ship or from a small boat.

Photographs of cetaceans were taken from the ship and from a small boat in order to verify stock identity and to document geographic variation. Individually identifiable whales were photographed for population studies.

Dipnet sampling for flying fish and other surface organisms was conducted for one hour at night (approximately hours 2000-2100 local time) concurrently with the evening CTD station.

Micronekton biomass between 0 and 500 m was sampled using active acoustics with a Simrad EQ50 echo sounder and two hull-mounted transducers. The echo sounder was operated continuously at 38 and 200 kHz, and interfaced to a data acquisition system. The EQ50 was operated continuously, except when the ship was in the area east of 115 W and between 5 to 20 N, when the transducer was turned off on alternating days in order to test whether transmission affected dolphin behavior and sighting rates.

Oceanographic data were collected throughout the survey. Two conductivity-temperature-depth (CTD) stations were scheduled every 24 hours: an hour before sunrise and an hour after sunset. A SeaBird CTD with General Oceanics rosette was used for these stations. From each cast, chlorophyll samples (to 150 meters) and salinity samples (0, 500, and 1000 meters or bottom) were collected and processed on board. Nutrient samples (0 - 500 meters) were collected, frozen, and stored for later analysis. Primary productivity was measured by 14C-uptake. Three expendable bathythermographs (XBT) were dropped daily while underway at 0900, 1200, and 1500 hours local time. Water samples for chlorophyll analysis and bucket temperatures were also collected daily, at 0900, 1200, 1500, and 1800 hours.

In the evening, up to four net sampling stations were conducted: a surface manta-tow for fifteen minutes following the post-sunset CTD station, a bongo net for 45 minutes to 200 meters following the completion of the manta tow, a ring net tow to 200 meters following the bongo tow, and a nekton trawl to 100 meters after the ring net tow.

RESULTS:

Observers visually surveyed 14,379 kilometers of trackline during the SPAM 1998 survey (Fig. 2). A total of 504 sightings of marine mammals were recorded, 439 of which were on-effort. The following tables display the preliminary data.

Table 4 - The number of sea turtles tagged, blood sampled, and skin biopsied per leg aboard the McArthur during the 1998 SPAM survey. All turtles were olive ridleys (Lepidochelys olivacea). No turtles were sampled on Legs 3 and 5.

Leg 1

Leg 2

Leg 4

Tag

Blood

Tag

Blood

Tag

Biopsy

5

5

5

5

1

1

Table 5 – Dipnet stations and total number of fish collected per leg aboard the McArthur during the 1998 SPAM survey.